I was recently trolling on Race-Dezert.com and found a thread about welding safety. A forum member found a warning on Brew Bikes' web site about the dangers of using brake cleaner to clean metal during welding prep.
In a nutshell, the story's author used brake cleaner to clean off a diesel fuel tank prior to doing some repair. Welding fuel tanks carries its own set of risks, but that's a subject for another time.
The rapid de-greasing and high evaporation rate of brake cleaner are two desirable qualities for cleaning metal. The problem was that a chlorinated brake cleaner was used this time.
There was a small amount of un-evaporated brake cleaner left on the surface, and when the heat of welding was brought to bear, the brake cleaner reacted with the welding heat and the argon shielding gas to produce the deadly gas phosgene. A few days later, the author found himself in the ICU.
He lived to tell about it, but you may not. Please be aware and cautious around chemicals and cleaners. Read the warning labels. They can save your health and your life.